I've been having birds arriving in my garden with their fronts "wetted" with glycerine from somebody's birdbath. I read somewhere that this could be bad for the birds if they digested too much but they also seem to take a long time to dry out.
What would be better for the birds....no liquid water for a few days (bearing in mind there's plenty of snow) or a glycerined supply.

Interesting dilema.
I don't like the thought of glycerine and what it could do to the plumage and oils in the plumage. Feather condition is crucial to survival. All the birds around here seemed very adept at eating snow for the water content.

I used some of the safe birdbath anti-freeze sold by CJ but it wasn't that great to be honest, it's not guaranteed at much below freezing.

I wouldn't think glycerine would be at all good for the birds - it would probably remove any natural waterproofing from their plumage. I just add CitroSan to my birdbath each time I clean and refill it, for hygiene, and I have added IceFree only the once, as it was just before the thaw began, so can't really say how good it is.